The Specific Aims will be: (a) accurate determination of the acid ionization constants (pK) and pH of common physiological bile acids in aqueous solutions from electromotive force methods on cells without liquid junction from 5 to 55 degrees C at 5 degree intervals including 37 degrees C; (b) the bile acids (8) to be studied are cholic, lithocholic, hyodeoxycholic, chenodeoxycholic, ursodeoxycholic, ursocholic (3Alpha-7Beta-12Alpha-trihydroxy-5Beta-cholanoic; and 3Beta-hydroxy-5Beta-cholanoic; and 7Alpha-hydroxy-5Beta-cholanoic acids); (c) to study the influence of added NaC1 (isotonic saline solution, 0.16 molal NaC1), and modified Krebs solution on the electrochemical properties of pK' and pH of 8 physiologically important bile acids at 5, 25, 37, and 55 degrees C; (d) determination of the dissociation constant and thermodynamic quantities of uric acid from 10 to 50 degrees C at 5 degree intervals including 37 degrees C using spectrophotometric method. The methodology involves two basic steps for parts (a)-(c) and one step for part (d): (1) The first step is the electromotive force measurements of the cell using Ag-AgC1 electrodes and hydrogen electrodes without liquid junction. (2) The second step is the determination of pK and pH values in isotonic saline solution (0.16 molal NaC1) and in a modified Krebs solution as a function of temperature. (3) For part (d), the optical absorbances of uric acid as a function of pH using HC1 solution in a media containing NaC1 and sodium acetate solution, will be measured. The long-term objectives are: (i) to provide accurate thermodynamic data for physiologically important bile acids and uric acid and their salts containing Na+,K+, as functions of temperature & ionic strength; (ii) to formulate the mechanism of acid-base equilibria with regard to hydrophobic-hydrophilic moieties of the steroids and structural changes due to aqueous (non-micellular acid (HA) solubility as well as the effect of added NaC1 on "salted in" and "salted out;" (iii) to eliminate the large uncertainties for the literature values of pK of uric acid, which are essential in the studies of gout, urolithiasis, and purine metabolism in the human body.